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Jan 28, 2015, 05:01 AM
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Connecting PSUs in parallel


Hi Everyone,

I am looking for some help wiring 2 server PSUs in parallel. I have 2 Dell 7950 units which are 12v and 750w each. I need a 12v 1500w output.

I've done some digging around on the excellent posts here but can't quite find a clear answer.

I think I've got it sussed, but would appreciate any input or advice from clever people!

Here is what I've come up with, basically, link the + and - outputs, and link the current share pins...any thoughts?

Link to image: gourmetpixel.com/tests/bens/sim_chair/dell-2950-parallel_guess.jpg

Thanks!
Ben
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Jan 28, 2015, 06:05 AM
ancora imparo
jj604's Avatar
Ben I think that is exactly what the current share pins are for but someone may be able to confirm for sure.
I can confirm that you should not remove the AC ground. In parallel the ground of each of the supplies are at the same ground potential. And serves as a safety as designed.
Jan 28, 2015, 10:35 AM
Registered User
Thanks jj604, I appreciate your input.
Jan 28, 2015, 12:24 PM
Registered User
You shouldn't really try running power supplies in parallel at all. They will not be stabilised and set up to deliver the exact same voltage. So if one is say .05V higher it will deliver all of the power... The other one will see no load.

But yes they should both be plugged in, earthed the same way, and just have outputs connected. Expect less power than you think!
Jan 28, 2015, 04:05 PM
Registered User
Actually server PSU's are designed to be run in parallel for redundancy purposes (if one dies, the other one takes all the load and keeps the server running - this also applies to when a circuit breaker trips or a power failure hits the area as 1 circuit will be on UPS power at a minimum).

By connecting the current share pin together the supplies will stabilise the voltage difference between them and share the load evenly.

Cheers
Whitedg
Jan 28, 2015, 08:45 PM
Registered User
vollrathd's Avatar
Quote:
Originally Posted by benjj
Hi Everyone,

I am looking for some help wiring 2 server PSUs in parallel. I have 2 Dell 7950 units which are 12v and 750w each. I need a 12v 1500w output.

I've done some digging around on the excellent posts here but can't quite find a clear answer.

I think I've got it sussed, but would appreciate any input or advice from clever people!

Here is what I've come up with, basically, link the + and - outputs, and link the current share pins...any thoughts?


Thanks!
Ben
The power supplies I've run across that are designed to be directly parallel connected will so indicate on their literature or documentation. If not documented, they may not be compatible with being parallel connected.
Jan 28, 2015, 08:50 PM
Registered User
Quote:
Originally Posted by jj604
Ben I think that is exactly what the current share pins are for but someone may be able to confirm for sure.
I can also confirm for sure. Connecting the +, -, and current share pins will indeed achieve the goal of sharing the load.

Note that in order to realize 1500 watt output you'll need a dedicated 110V, 20A circuit or (even better) a 220V circuit. Attempting to draw 1500 watts from a DC supply that's connected to a standard 110V, 15A circuit will likely exceed the capability of the circuit and pop a breaker.

Mark
Jan 28, 2015, 08:57 PM
ancora imparo
jj604's Avatar
Unfortunately the key problem is that server supplies are never documented. At least, almost never, unless you can find access to a "Level 1" Service Facility or are one.
Unlike a commercial PS, they are never intended to be sold as a stand alone unit but only as a replacement part. Hence there is no requirement on the supplier to document their configuration or performance. We are fortunate in some cases that pin outs have been extracted from service manuals, but that's about it.
.
That's why we have such a vigorous thread on these supplies.

My money is on the sharing pins doing exactly what the OP requires for exactly the reasons explained by whitedg.
UPDATE: see Mark posted while I was typing!
John
Quote:
Originally Posted by vollrathd
The power supplies I've run across that are designed to be directly parallel connected will so indicate on their literature or documentation. If not documented, they may not be compatible with being parallel connected.
Jan 29, 2015, 05:16 AM
Registered User
Excellent help, cheers everyone.

Looks like I am good to try then. I live in the UK so I have 240v 13amp sockets.

I am also working in my garage which has an isolated circuit, so I won't blow up the house and upset my wife trying to watch TV
Last edited by benjj; Jan 29, 2015 at 10:13 AM.
Jan 29, 2015, 05:44 AM
ancora imparo
jj604's Avatar
Been there, done that - but only once!!

Then when we had the house rewired with 3 phase, I got the garage put on its own phase. If necessary with enough outlets on separate CBs I can pull 60 Amps at 240V and never even disturb the General Manager, Domestic Affairs.

Quote:
Originally Posted by benjj
Excellent help, cheers everyone.

Looks like I am good to try then. I live in the UK so I have 240v 13amp sockets.

I am also working in my garage which has an isolated circuit, so I won't blow up the house and upset my wire trying to watch TV
Feb 05, 2015, 04:27 AM
Registered User
Update time.

I wired this all up last night and nothing went bang

I ran the rig for a few hours and everything is looking great. No melting, no smoke, no warning lights....

And a LOT of juice!!! Amazing.

It's wired up exactly as my first diagram. No modded power plugs, no shared pin ground and connected current share pin.

Thanks to anyone who put some help my way. Hope this post helps people in the future.
Feb 05, 2015, 06:58 AM
ancora imparo
jj604's Avatar
Good news. Congratulations.
Dec 27, 2015, 12:34 PM
Registered User

Ditto


Quote:
Originally Posted by benjj
Update time.

I wired this all up last night and nothing went bang

I ran the rig for a few hours and everything is looking great. No melting, no smoke, no warning lights....

And a LOT of juice!!! Amazing.

It's wired up exactly as my first diagram. No modded power plugs, no shared pin ground and connected current share pin.

Thanks to anyone who put some help my way. Hope this post helps people in the future.
Hi Benjj,

I also have 2x 2950 N750P-SO units on their way and just wanted to ask about the ground.

I watched this video...
1000 Watt Power Supply Build Guide iCharger 306B EP Buddy Parallel Board Deans (14 min 47 sec)
in which he breaks the DC ground in one unit so they can touch. I know they are HP units but did you open the cases and do any mods in side ? Or is this taken care of by linking the current share ?

If you have picture(s) of the final unit that would be awesome

Happy Christmas & HNY.

Many thanks

Andrew - P.S I'm in the UK 240V club also.


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